The present invention relates to a method and apparatus for minimizing the power induced in a moving or stationary flat conducting product which is maintained in position without contact by electromagnetic forces.
The present invention is applicable, in particular, to finishing operations such as heat treatment and, in general, when it is necessary to displace or to maintain conducting products without contact and without heating.
Known ways of displacing or maintaining flat, conducting products without contact by means of electromagnetic forces have the disadvantage of inducing an appreciable (non-negligible) degree of heating. They generally comprise a single inductor I placed under the product P to be displaced or maintained without contact (see FIG. 1 of the drawings attached hereto), with the intensity and frequency of the magnetic field being adapted to the physical properties and the dimensions of the product.
The method and apparatus which are the object of the present invention, make it possible to considerably reduce the heating induced in a moving or stationary flat, conducting product which is subjected to electromagnetic forces in order to maintain it in a position, i.e. guide it and levitate it, without contact.
The method comprises subjecting the product in certain zones of the two opposing alternating magnetic fluxes essentially equivalent to each other and perpendicularly disposed relative to the corresponding surface of the product in the zones, so that in each of the zones, with the product in a position of equilibrium, the component of the magnetic flux of the resultant field perpendicular to each zone is minimal and the components parallel to each zone are at a maximum, by virtue of a deflection of the two fluxes.
Apparatus suitable to perform the method comprises, for each zone wherein electromagnetic forces are induced, at least one pair of inductors, each with several poles, the polar surfaces of which are essentially parallel to a surface of the product in each zone, the two inductors of the pair being placed in a manner essentially symmetrical with respect to a location in the zone corresponding to the desired equilibrium position of the product, with the poles of the inductors facing each other in pairs on either side of the product being maintained instantaneously at the same polarity and with the fluxes passing through them being of essentially the same magnitude.
In a particular embodiment especially but not exclusively suitable for the treatment of strip, each of the inductors comprises successive poles of an elongated form, which are alternatingly North and South at a given instant.
In a further embodiment, particularly but not exclusively well suited for the treatment of sheet or plate, each of the inductors comprises identical poles placed regularly in keeping with an identical polar pitch in two orthogonal directions. In each of the two directions, at each instant, successive poles are alternatingly North and South.